This present invention relates to a distance measurement method and apparatus and a relative position measurement apparatus, and more particularly, to a method and apparatus for measuring distance to a target object using pseudo noises which are represented by maximal sequence codes, and to an apparatus for measuring relative position of an operator with respect to a device.
It is known that distance to a target object can be measured using maximal-sequence codes which are a variety of pseudo noises.
FIG. 11 is a block diagram schematically showing an arrangement of a conventional distance measurement apparatus. A carrier signal which is output from a carrier signal generator is supplied to a balanced modulator, and a maximal-sequence code which is output from a maximal-sequence code generator is also supplied to the balanced modulator to modulate the carrier signal with the maximal-sequence code. The modulated carrier signal is radiated to a target object by a transducer. The modulated carrier signal is reflected by the target object and received by a receiver. The received signal is supplied to a balanced mixer to which a maximal-sequence code is supplied through a variable delay unit, to obtain an inpulse response. An inpulse response signal is supplied to a distance counter through a synchronous detector. The maximal-sequence code output from the variable delay unit is also supplied to the distance counter and the maximal-sequence code is directly supplied to the distance counter so as to measure the distance to the target object.
That is, a cross-correlation of a reflected maximal-sequence code which is obtained by radiating a standard maximal-sequence code and reflecting of the code by the target object with maximal-sequence codes which are obtained by shifting the standard maximal-sequence code with every 1 bit, is obtained. Then, a propagation delay time of the maximal-sequence code is obtained based upon a maximal-sequence code with a predetermined number of bits shifted to obtain the maximum cross-correlation value. Thereafter, the distance to the target object is measured based upon the obtained propagation delay time and a known wave propagation delay time.
Furthermore, noise influence is effectively reduced so as to provide remarkably accurate distance measurements without strengthening the radiated maximal-sequence code because the maximal-sequence code has significant auto-correlation characteristics. The maximal-sequence code can easily be lengthened in code length and noise influence can be reduced further as a result of code length lengthening, thereby the desired distance measurement accuracy can be easily obtained. That is, a distance resolution .DELTA.l is expressed by the equation of .DELTA.l.ltoreq.CT/L (meters), and the distance resolution can be lesser by making the L longer. Where, a propagation velocity is C m/sec., the code length is L bits and 1 cycle of the maximal-sequence code is T sec.
Cross-correlation values of the reflected maximal-sequence code with a plurality of species of shifted maximal-sequence codes corresponding to the code length are necessarily calculated because the maximum cross-correlation value must be detected. This has the disadvantage of remarkably lengthening the necessary time period for distance measurement. The disadvantage becomes more and more conspicuous with further improvement in distance measurement accuracy.
The disadvantage can be eliminated by providing cross-correlators for obtaining cross-correlation values based upon every shifted maximal-sequence code corresponding to the code length. The further disadvantage of enlargement of the distance measurement apparatus is arisen because the number of cross-correlators is remarkably increased.
In both distance measurement apparatus, when the apparatus are used under circumstances of multipath reflection, maximum cross-correlation values are detected for every reflection path. This is disadvantageous because measuring the distance to the target object with accuracy becomes very difficult.
Conventionally in a three-dimensional graphics display apparatus, stereoscopic vision is employed so as to give a feeling of realness to display figures. But sufficient realness may not be obtained by employing only stereoscopic vision. Consequently, it is demanded that a perspective projection of the display figure with respect to the viewing direction be obtained based upon the detected relative positions of the operator and the display.
To satisfy the demand, a method may be employed in which distance measurements based upon a pulse echo method using ultrasonic waves are performed at different positions in a three-dimensional graphics display apparatus. Then, the relative position of the operator is measured based upon the plural distance measurement results. When distance measurement based on the pulse echo method using ultrasonic waves is performed, disadvantages arise in that malfunctions caused by noise output from office automation apparatus may occur, in that malfunctions of sound input interfaces may occur, and in that malfunctions caused by multipath reflection and the like may occur because the effective range of distance measurement cannot be limited to a neighbouring graphics display apparatus and that interference with another interface employed in the same manner cannot be avoided. As a result, measuring the accurate relative position of the operator with respect to the graphics display apparatus becomes almost impossible.
To eliminate these disadvantages, a method may be employed in which a carrier signal is modulated with pseudo noise and radiated, then a received signal is demodulated in the graphics display apparatus. But another disadvantage arises in that the time period necessary for distance measurement is lengthened by calculation of cross-correlation values for the received signal with every shifted maximal-sequence code corresponding to the code length, because the maximum cross-correlation value must be detected in the receiving side. The disadvantage becomes more and more conspicuous with the improvement of accuracy of the distance measurement. Display speed of the graphics display apparatus is remarkably lowered, accordingly.
The disadvantage can be eliminated by providing cross-correlators for obtaining cross-correlation values based upon every shifted maximal-sequence code corresponding to the code length. The further disadvantage of enlargement of the distance measurement apparatus arises because the number of cross-correlators is remarkably increased.
In both distance measurement apparatus, when the apparatus are used under a circumstance with multipath reflection, maximum cross-correlation values are detcted for every reflection path, thereby the disadvantage arises that measuring the distance to the target object with accuracy becomes very difficult.
As a result, in a three-dimensional graphics display apparatus, it is not performed at all that a relative position (viewing direction to a scope and the like) of an operator is automatically measured, a viewing direction is calculated based upon the measurement result and then a perspective projection and the like of display figures is changed in correspondence with the viewing direction.
In apparatus, which are preferably controlled based upon a detected relative position of an operator with other than the graphics display apparatus, similar disadvantages as mentioned above, arise.